If you are replying to the question in the thread title, it said habitable, not with life.If you mean habitable for humans, no planet on which long-term human survival can take place has ever been found. Only one planet with habitable atmosphere has ever been found, and i believe that was at -70 degrees Celcius.

Source of the post I see. My arrogance led me to assume human life. Yes, of course, those little pioneers can eke out a living just about anywhere.

Yeah. Considering life on Earth came into existence about as soon as it could, and unicellular organisms can live everywhere, life may be much more common than we think.

Then that should make us hopeful for Mars, Europa and Enceladus.

I don't know about Europa and Enceladus, but I'm pretty sure you're very correct about being hopeful about Mars. Thanks to extremephiles and the fact that it's very hard to completely sterilize things, I think there might be (Earth) life on Mars!

Well, about the original question, it might be possible for even a lone rouge planet to be habitable. I'm imagining it would have either a hot core to warm things up for liquid water, or have enough really heavy elements that this happens often enough to keep the planet warm. Of course, the second option would be rare (and might kill the life), and the planet wouldn't stay habitable for quite as long as it would be if it was orbiting a star, but it still would count.

Maybe it's for the better. You wouldn't want somebody hopping aboard a nearby free-floating planet and shuttling off to Andromeda

I wonder what life would be like on such a planet? Soaring endlessly through space, hoping no asteroids get in your way. The day-night cycle would be ridiculous, though I suppose it wouldn't be too bad to awaken each day to a new sky. Hopefully not one with a magnetar or a black hole in the middle.

As far as i know, most asteroids are in star systems, and even if 100% of asteroids was in interstellar space i don't think they would be a big concern simply because space is much much much larger than humans can comprehend.

The surface would be very close to absolute zero, which means that almost all gases commonly found in atmospheres are liquids or solids (oxygen and nitrogen included). Life could live under the surface where there could be liquid water and volcanoes that provide heat.